Recent drastic progress of magnetic recording technologies provides large-volume drives, resulting in higher recording densities of magnetic recording media. However, if a higher recording density were sought in magnetic recording media of an longitudinal magnetic recording system widely used at present, recording bits would have to be too small to record by a recording head, needing much higher coercivity. Accordingly, investigation has been conducted to provide a perpendicular magnetic recording system to increase a recording density.
The perpendicular magnetic recording system uses a magnetic film having an easy axis of magnetization orientated in a perpendicular direction to the recording surface, suffering from little decrease in read-write characteristics because of small demagnetization in bits in a high recording density, and thus suitable for a high recording density. A two-layer recording medium having a magnetic recording layer and a soft magnetic layer for an increased recording sensitivity has been developed for the perpendicular magnetic recording system. As the soft magnetic film of the two-layer recording medium, the use of a soft magnetic film of an Fe—Co—B alloy has been proposed (see US 2002/0058159A1).
Development has been actively conducted recently to provide magnetoresistive random access memories (MRAMs), etc. as devices comprising tunnel magnetoresistive (TMR) elements. The use of the soft magnetic Fe—Co—B alloy film for such TMR device has been proposed (see JP 2003-304010 A).
A magnetron sputtering method is generally used for the formation of soft magnetic films for the two-layer media and soft magnetic films for the TMR devices. The magnetron sputtering method is a method in which a magnetic flux is leaked from a magnet disposed on the back of the target to a target surface, and a plasma is focused in the leaked magnetic flux region, to achieve a high-speed film formation. Accordingly, if the target had high permeability, a sufficient leaked magnetic flux would not be formed on the target surface. Accordingly, the target should have as small permeability as possible.